Re: hda: error: DMA in progress..

[Jens Axboe]

On Fri, Jun 21 2002, Jens Axboe wrote:
> > And now we see that it is indeed apparently really interacting with
> > the TCQ code in bad ways. But if I look down from the above code (Just 
> > below in ide.c)
> > 
> > 	if (blk_queue_plugged(&drive->queue)) {
> > 			BUG_ON(!drive->using_tcq);
> > 			break;
> > 		}
> > 
> > It seems like the check which is catching reality right now
> > is bogous in itself. Becouse having DMA running would be
> > only problematic if the queue was still plugged. (Right?)
> > So please just disable the check.
> 
> Not exactly, let me see if I remember the race here... The queue can
> become plugged when we queue one request with the drive (the only on the
> queue at that time), and then try to queue another right after (hence
> only a tcq issue). In that time period, we drop the queue lock, so it's
> indeed possible for the block layer to plug the queue before we reach
> the above code again. The drive can be in two states here, 1) IDE_DMA is
> set because the drive didn't release the bus (or it did, and it already
> reconnected), or 2) drive is disconnected from the bus.

Sorry that's not true (#1), it's _never_ valid for IDE_DMA to be set
here even when using TCQ (less so, if possible, for non-tcq :-). At
least according to the old semantics. That's only the case when using
speculative starts of the dma engine for tcq with release interrupt
enabled, which we don't use on Linux.

-- 
Jens Axboe